The first thing to do is to learn the load capacity of the current tires.
Then get the RV on a truck scale when the RV is at it's heaviest (most water, propane, food & clothes.
You MUST have tires capable of supporting the actual measured load.
I have a number of posts on tire loading and weight on my blog. See link in signature.
Retired Tire Design Engineer (40 years). I write a blog on RV tire applications www.RVTireSafety.NET and give seminars on RV tire application across the US. Serve on Technical Advisory Panel for FMCA.